1. Field of the Invention
Embodiments of the present invention generally relate to handling tubulars. More specifically, embodiments of the present invention relate to connecting and lowering tubulars into a wellbore.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. In drilling operations, a drilling rig is supported by the subterranean formation. A rig floor of the drilling rig is the surface from which tubular strings, cutting structures, and other supplies are lowered to ultimately form a subterranean wellbore lined with casing. A hole is formed in a portion of the rig floor above the desired location of the wellbore. The axis that runs through the center of the hole formed in the rig floor is well center.
Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on the drilling rig. After drilling to a predetermined depth, the drill string and drill bit are removed and a section or string of casing is lowered into the wellbore.
Often, it is necessary to conduct a pipe handling operation to connect sections of casing to form a casing string which extends to the drilled depth. Pipe handling operations require the connection of casing sections to one another to line the wellbore with casing. The casing string used to line the wellbore includes casing sections (also termed “casing joints”) attached end-to-end, typically by threaded connection of male to female threads disposed at each end of a casing section. To install the casing sections, successive casing sections are lowered longitudinally through the rig floor and into the drilled-out wellbore. The length of the casing string grows as successive casing sections are added.
When the last casing section is added, the entire casing string must be lowered further into its final position in the wellbore. To accomplish this task, drill pipe sections (or “joints”) are added end-to-end to the top casing section of the casing string by threaded connection of the drill pipe sections. The portion of the tubular string which includes sections of drill pipe is the landing string, which is located above the portion of the tubular string which is the casing string. Adding each successive drill pipe section to the landing string lowers the casing string further into the wellbore. Upon landing the casing string at its proper location within the wellbore, the landing string is removed from the wellbore by unthreading the connection between the casing string and the landing string, while the casing string remains within the wellbore.
Throughout this description, tubular sections include casing sections and/or drill pipe sections, while the tubular string includes the casing string and the drill pipe string. To threadedly connect the tubular sections, each tubular section is retrieved from its original location on a rack beside the drilling platform and suspended above the rig floor so that each tubular section is in line with the tubular section or tubular string previously disposed within the wellbore. The threaded connection is made up by a device which imparts torque to one tubular section relative to the other, such as a power tong or a top drive. The tubular string formed of the two tubular sections is then lowered into the previously drilled wellbore.
The handling of tubular sections has traditionally been performed with the aid of a spider along with an elevator. Spiders and elevators are used to grip the tubular sections at various stages of the pipe handling operation. In the making up or breaking out of tubular string connections between tubular sections during the pipe handling operation, the spider is typically used for securing the tubular string in the wellbore. Additionally, an elevator suspended from a rig hook is used in tandem with the spider. In operation, the spider remains stationary while securing the tubular string in the wellbore. The elevator positions a tubular section above the tubular string for connection. After completing the connection, the elevator pulls up on the tubular string to release the tubular string from the slips of the spider. Freed from the spider, the elevator may now lower the tubular string into the wellbore. Before the tubular string is released from the elevator, the spider is allowed to engage the tubular string again to support the casing string. After the load of the tubular string is switched back to the spider, the elevator may release the tubular string and continue the makeup process with an additional tubular section.
The elevator is used to impart torque to the tubular section being threaded onto the tubular section suspended within the wellbore by the spider. To this end, a traveling block suspended by wires from a draw works is connected to the drilling rig. A top drive with the elevator connected thereto by elevator links or bails is suspended from the traveling block. The top drive functions as the means for lowering the tubular string into the wellbore, as the top drive is disposed on rails so that it is moveable longitudinally upward and downward from the drilling rig along the rotational axis of well center. The top drive includes a motor portion used to rotate the tubular sections relative to one another which remains rotationally stationary on the top drive rails, while a swivel connection between the motor portion and the lower body portion of the top drive allows the tubular section gripped by the elevator to rotate. The rails help the top drive impart torque to the rotating tubular section by keeping the top drive lower body portion rotationally fixed relative to the swivel connection. Located within the rig floor is a rotary table into or onto which the spider is typically placed.
Recently, it has been proposed to use elevators to perform the functions of both the spider and the elevator in the pipe handling operation. The appeal of utilizing elevators for both functions lies in the reduction of instances of grippingly engaging and releasing each tubular section with the elevator and the spider which must occur during the pipe handling operation. Rather than releasing and gripping repeatedly, the first elevator which is used to grip the first casing section initially may simply be lowered to rest on the hole in the rig floor. The second elevator may then be used to grip the second casing section, and may be lowered to rest on the hole in the rig floor.
To accomplish this pipe handling operation only with elevators, the first elevator must somehow be removed from its location at the hole in the rig floor to allow the second elevator to be lowered to the hole. This removal is typically accomplished by manual labor, specifically rig personnel physically changing the location of the first elevator on the rig floor. Furthermore, the purely elevator pipe handling operation requires attachment of the elevator links to each elevator when it is acting as an elevator, as well as detachment of the elevator links from each elevator when it is acting as a spider. This attachment and detachment is also currently accomplished using manual labor. Manipulation of the elevator links and the elevator by manual labor is dangerous for rig personnel and time consuming, thus increasing well cost.
Manual labor is also used to remove the elevator or elevator slips (described below) when it is desired to lower the tubular, as well as replace the elevator or elevator slips when it is desired to grippingly engage the tubular. Manually executing the pipe handling operation is dangerous to personnel and time consuming, thus resulting in additional overall cost of the well.
Sometimes a false rotary table is mounted above a rig floor to facilitate wellbore operations. The false rotary table is an elevated rig floor having a hole therethrough in line with well center. The false rotary table allows the rig personnel to access tubular strings disposed between the false rotary table and the rig floor during various operations. Without the false rotary table, access to the portion of the tubular string below the gripping point could only be gained by rig hands venturing below the rig floor, which is dangerous and time-consuming. Manual labor is currently used to install and remove the false rotary table during various stages of the operation.
Typically, a spider includes a plurality of slips circumferentially surrounding the exterior of the tubular string. The slips are housed in what is commonly referred to as a “bowl”. The bowl is regarded to include the surfaces on the inner bore of the spider. The inner sides of the slips usually carry teeth formed on hard metal dies for grippingly engaging the inside surface of the tubular string. The exterior surface of the slips and the interior surface of the bowl have opposing engaging surfaces which are inclined and downwardly converging. The inclined surfaces allow the slip to move vertically and radially relative to the bowl. In effect, the inclined surfaces serve as a camming surface for engaging the slip with the tubular string. Thus, when the weight of the tubular string is transferred to the slips, the slips will move downwardly with respect to the bowl. As the slips move downward along the inclined surfaces, the inclined surfaces urge the slips to move radially inward to engage the tubular string. In this respect, this feature of the spider is referred to as “self tightening.” Further, the slips are designed to prohibit release of the tubular string until the tubular string load is supported by another means such as the elevator. The elevator may include a self-tightening feature similar to the one in the spider.
When in use, the inside surfaces of the currently utilized slips are pressed against and “grip” or “grippingly engage” the outer surface of the tubular section which is surrounded by the slips. The tapered outer surface of the slips, in combination with the corresponding tapered inner face of the bowl in which the slips sit, cause the slips to tighten around the gripped tubular section such that the greater the load being carried by that gripped tubular section, the greater the gripping force of the slips being applied around that tubular section. Accordingly, the weight of the casing string, and the weight of the landing string being used to “run” or “land” the casing string into the wellbore, affects the gripping force being applied by the slips, as the greater the weight of the tubular string, the greater the gripping force and crushing effect on the drill pipe string or casing string.
A significant amount of oil and gas exploration has shifted to more challenging and difficult-to-reach locations such as deep-water drilling sites located in thousands of feet of water. In some of the deepest undersea wells, wells may be drilled from a drilling rig situated on the ocean surface several thousands of feet above the sea floor, and such wells may be drilled several thousands of feet below the sea floor. It is envisioned that as time goes on, oil and gas exploration will involve the drilling of even deeper holes in even deeper water.
For many reasons, the casing strings required for such deep wells must often be unusually long and have unusually thick walls, which means that such casing strings are unusually heavy and can be expected in the future to be even heavier. Additionally, the landing string needed to land the casing strings in such extremely deep wells must often be unusually long and strong, hence unusually heavy in comparison to landing strings required in more typical wells. Hence, prior art slips in typical wells have typically supported combined landing string and casing string weights of hundreds of thousands to over a million pounds, and the slips are expected to require the capacity to support much heavier combined weights of casing strings and landing strings with increasing time.
Prior art slips used in elevators and spiders often fail to effectively and consistently support the combined landing string and casing string weight associated with extremely deep wells because of numerous problems which occur at such extremely heavy weights. First, slips currently used to support heavy combined landing string and casing string weights apply such tremendous gripping force due to the high tensile load that the slips must support that the gripped tubular section may be crushed or otherwise deformed and thereby rendered defective. Second, the gripped tubular section may be excessively scarred and thereby damaged due to the teeth-like grippers on the inside surface of the slips being pressed too deeply into the gripped tubular section. Furthermore, the prior art slips may experience damage due to the heavy load of the tubular string, thereby rendering them inoperable or otherwise damaged.
A related problem involves the often uneven distribution of force applied by the prior art slips to the gripped tubular section. If the tapered outer wall of the slips is not maintained substantially parallel to and aligned with the tapered inner wall of the bowl, the gripping force of the slips may be concentrated in a relatively small portion of the inside wall of the slips rather than being evenly distributed throughout the entire inside wall of the slips, possibly crushing or otherwise deforming the gripped tubular section or resulting in excessive and harmful strain or elongation of the tubular string below the point at which the tubular string is gripped. Additionally, the skewed concentration of gripping force may cause damage to the slips, rendering them inoperable or otherwise damaged. Rough wellbore operations may cause the slips and/or bowl to be jarred, resulting in misalignment and/or irregularities in the tapered interface between the slips and the bowl to cause the uneven gripping force. The uneven distribution of gripping force problem is exacerbated as the weight supported by the slips is increased.
It is therefore desirable to provide a method and apparatus for supporting the weight of the tubular string during pipe handling operations with minimal crushing, deforming, scarring, or stretching-induced elongation of the tubular string. It is further advantageous to provide a fully automated tubular handling and tubular running apparatus and method. There is a further need for apparatus and methods for utilizing a pipe handling system using elevators for the functions of both the elevator and the spider which are safer and more efficient than current apparatus or methods in use.